1. Field of the Invention
The present invention relates to a camera having a line of sight detecting apparatus for detecting a line of sight of an observer.
2. Related Background Art
Hitherto, the assignee of the present invention has proposed various apparatuses for detecting which position on an observing surface an observer or a photographer is observing, namely, for detecting what is called a line of sight (U.S. patent Ser. Nos. 327784, 475756, 584896, and 406588).
Parallel light fluxes from a light source are projected to a front eye part of the eyeball of the observer and the visual axis is obtained by using a Purkinje image by the reflected light from the cornea and an image forming position of the pupil.
FIGS. 5A and 5B are diagrams for explaining the principle of a line of sight detecting method. FIG. 5A is a schematic diagram of a line of sight detection optical system and FIG. 5B is a diagram showing an output intensity of a photoelectric conversion element array 6.
In the diagrams, reference numeral 5 denotes a light source such as a light emitting diode or the like for emitting an infrared light which is not sensed by an observer. The light source 5 is arranged on a focal point surface of a light projection lens 3.
The infrared light emitted from the light source 5 is converted into the parallel light by the light projection lens 3 and is reflected by a half mirror 2 and irradiates a cornea 21 of the eyeball. At this time, a Purkinje image d (virtual image) by a part of the infrared light reflected by the surface of the cornea 21 passes through the half mirror 2 and is converged by a light, reception lens 4 and is projected to a position Zd' on the photoelectric conversion element array 6.
The light fluxes from edge portions a and b of an iris 23 are transmitted through the light reception lens 4 and images of the edge, portions a and b are formed at positions Za' and Zb' on the photoelectric conversion element array 6. In the case where a rotational angle .theta. of an optical axis K of the eyeball for an optical axis J of the light reception lens 4 is small, coordinates Z.sub.c of a center position c of a pupil 24 are expressed by EQU Z.sub.c .perspectiveto.(Z.sub.a +Z.sub.b)/2
by assuming that Z coordinates of the edge portions a and b of the iris 23 are set to Z.sub.a and Z.sub.b.
On the other hand, since the Z coordinates of the Purkinje image d coincide with the Z coordinates of a center O of the radius of curvature of the cornea 21, the rotational angle .theta. of the eyeball optical axis K in which the Z coordinates of the generating position d of the cornea reflection image are set to Z.sub.d and a distance between the center O of the radius of curvature of the cornea 21 and the center C of the pupil 24 is set to OC almost satisfies the following relational equation. EQU OC*sin.theta..perspectiveto.Z.sub.c .noteq.Z.sub.b ( 1)
Therefore, in a central processing unit (CPU) 9, by detecting the positions of the singular points Purkinje image d and edge portions a and b of the iris) projected onto the photoelectric conversion element array 6 as shown in FIG. 5B, the rotational angle .theta. of the eyeball optical axis K can be obtained. At this time, the equation (1) is rewritten an follows. EQU .beta.*OC* sin.theta..perspectiveto.(Z.sub.a '+Z.sub.b ')/2-Z.sub.d '(2)
where, .beta. is a magnification which is determined by the position of the eyeball relative to the light reception lens 4.
Further, when the rotational angle .theta. of the eyeball optical axis of the observer is calculated, by correcting the optical axis pf the eyeball and the line of sight, the line of sight of the observer can be obtained.
On the other hand, although the diagrams show an example in the case where the eyeball of the observer rotates in the Z-X plane (for instance, horizontal plane), the line of sight can be also similarly detected in the case where the eyeball of the observer rotates in the X-Y plane (e.g., vertical plane).
FIG. 6 is a schematic diagram showing a main section in the case where the line of sight detecting apparatus is arranged in a single-lens reflex camera. An object light which has been transmitted through a photographing lens 101 is reflected by a lift-up mirror 102 and forms an image at a position near a focal point surface of a focusing plate 104. The object lights diffused by the focusing plate 104 are, further led to an eye point X of a photographer through a condenser lens 105, a pentagonal lens 106, and an ocular lens 1.
A line of sight detection optical system is constructed by: an illumination optical system comprising the light source 5 such as an infrared light emitting diode or the like which is not sensed for a photographer (observer) and the light projection lens 3; and a light reception optical system comprising the photoelectric conversion element array 6 and the light reception lens 4. The line of sight detection optical system is arranged above the ocular lens 1 also serving as a dichroic mirror. An infrared light emitted from the infrared light emitting diode 5 is reflected by a dichroic mirror surface la and illuminates the eyeball of the photographer. Further, a part of the infrared light reflected by the eyeball is again reflected by the dichroic mirror surface la and is converged onto the photoelectric conversion element array 6 through the light reception lens 4. The direction of the line of sight the photographer is calculated by the CPU 9 on the basis of the image information (FIG. 5B) of the eyeball derived on the photoelectric conversion element array 6.
In the single-lens reflex camera, if it is known which point on the focal surface the photographer is observing as mentioned above, for instance, in the case of a camera having a focal point detecting apparatus which can detect a plurality of focal points in the finder screen, when the photographer intends to execute an automatic focal point detection by selecting one point which coincides with a main object, that is, an object to be photographed by the photographer, the operation to select and input such a single point is omitted and such a point is regarded as a point which the photographer is observing and such a point is automatically selected. The above method is effective to execute the automatic focal point detection.
However, in the recent single-lens reflex camera, generally, a zoom lens is attached and used. When the photographer executes a zooming, the position of the object in the finder screen is also moved during the zooming operation. In many cases, the position during the zooming doesn't coincide with the position of the object after completion of the zooming. Therefore, the motion of the line of sight during the zooming doesn't reflect the position of the line of sight after the zooming. There is a drawback such that if the camera is controlled by using the line of sight data obtained during the zooming, for instance, if a focal detection point is selected, an erroneous point is selected.
Further, to select a plurality of focal detection points or determine an exposure value from photometric values of a plurality of areas, it is necessary to detect one or more positions of the main object which the photographer wants to photograph. To accurately detect the positions of the main object which the photographer desires to photograph from the motion of the line of sight, such a position must be statistically detected from a plurality of line of sight information. Therefore, not only the line of sight is detected but also the visual axis information must be stored. If the zooming operation is performed during the accumulation of such information, the position of the main object is detected in a state in which the line of sight information for the position of the main object before the zooming which is different from the position of the main object after the zooming operation has also been accumulated, so that there is a drawback such that the position of the main object is erroneously detected.
In addition, in the case where the photographer who has been executing the photographing in an automatic focusing (AF) mode using the line of sight information tries to execute a focusing operation by changing the operating mode from the AF mode to the photographing operation in a manual focusing mode or a power focusing mode during the photographing operation, the line of sight information is unnecessary in both of the above focusing modes, so that the photographer needs to further execute an operation to stop the line of sight detection and there is a drawback such that the operation of the camera becomes complicated.
On the other hand, when a focal point of the point corresponding to the position of the main object (main line of sight) obtained from the visual axis information is detected and a focal point adjustment of the focusing lens is performed from a defocusing amount at such a point, the information is unnecessary during the driving of the lens to adjust the focal point of the focusing lens. In addition, even if the line of sight information obtained during the driving of the focusing lens is not used as position information upon execution of the focal point detection, there is a drawback such that the execution of the line of sight detection causes energy to be consumed in vain.
During the driving of the focusing lens, a display state in the finder is changing (that is, the focal point is changing). As a line of sight in such a state, in many cases, an object other than the main object is seen, so that there is a possibility such that erroneous information is obtained.